1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a main pole and a shield.
2. Description of Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head includes a main pole that produces a write magnetic field in a direction perpendicular to the plane of the recording medium. The main pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces the recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a generally constant width. To achieve higher recording density, it is required that the write head of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air outflow end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erasure). For higher recording densities, it is necessary to prevent the adjacent track erasure.
To prevent the adjacent track erasure induced by a skew and provide improved recording densities, it is effective to provide one or more shields in the vicinity of the main pole so as to be adjacent to the main pole with a gap part interposed therebetween. For example, U.S. Pat. No. 6,954,340 B2 and U.S. Patent Application Publication No. 2005/0128637 A1 describe a magnetic head including four shields: one having an end face located in the medium facing surface at a position forward of an end face of the main pole in the direction of travel of the recording medium; another having an end face located in the medium facing surface at a position backward of the end face of the main pole in the direction of travel of the recording medium; and the other two having two end faces located in the medium facing surface at positions on opposite sides of the end face of the main pole in the track width direction. The end faces of the four shields are arranged to wrap around the end face of the main pole in the medium facing surface.
In a magnetic head, a position that is forward of the main pole in the direction of travel of the recording medium is a position on the air-outflow-end side (the trailing end side), whereas a position that is backward of the main pole in the direction of travel of the recording medium is a position on the air-inflow-end side (the leading end side). Hereinafter, a shield having an end face located forward of the end face of the main pole in the direction of travel of the recording medium will be referred to as a trailing shield, and a shield having an end face located backward of the end face of the main pole in the direction of travel of the recording medium will be referred to as a leading shield.
A magnetic head having a shield is typically provided with a return path section for connecting the shield and part of the main pole away from the medium facing surface to each other. In addition, a coil is provided to pass through a space defined by the main pole, the gap part, the shield, and the return path section. The shield and the return path section function to capture a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, and to thereby prevent the magnetic flux from reaching the recording medium. The shield and the return path section also function to allow a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole. The magnetic head having the shield and the return path section is capable of preventing adjacent track erasure and provides a further improved recording density.
JP-A-2006-48921A discloses a technology for reducing noise caused by a magnetic flux in a backing layer of a recording medium for a magnetic head having a main pole and at least one auxiliary pole. The magnetic head is provided with a trailing-side exciting coil and a leading-side exciting coil disposed with the main pole therebetween. The two exciting coils are designed to have different numbers of turns so as to produce different magnetomotive forces. JP-A-2006-48921A further discloses an example of the magnetic head including a trailing-side auxiliary pole and a leading-side auxiliary pole disposed with the main pole therebetween. In the magnetic head, the trailing-side exciting coil is disposed between the main pole and the trailing-side auxiliary pole, and the leading-side exciting coil is disposed between the main pole and the leading-side auxiliary pole, with the number of turns of the leading-side exciting coil made greater than that of the trailing-side exciting coil.
The position of an end of a record bit to be recorded on the recording medium depends on the position of an end of the end face of the main pole located in the medium facing surface, the end being located forward in the direction of travel of the recording medium. In order to define the position of the end of the record bit accurately, it is therefore effective to provide the trailing shield, in particular.
In addition, as the frequency of the recording signal is increased in order to increase the recording density, the magnetic head is required to be improved in the rate of change in the direction of the magnetic flux produced from the end face of the main pole. To satisfy this requirement in the magnetic head having the trailing shield, it is particularly effective to reduce the length of a magnetic path that passes through the trailing shield and the main pole. To this end, it is effective to provide a return path section that is located forward of the main pole in the direction of travel of the recording medium and connects the trailing shield and part of the main pole away from the medium facing surface to each other (such a return path section will hereinafter be referred to as the trailing return path section) and to reduce the number of turns of the coil that passes through the space defined by the main pole, the gap part, the trailing shield, and the trailing return path section. However, this would cause a shortage of magnetomotive force produced by the coil, thereby hindering the main pole from producing a write magnetic field of sufficient magnitude.
It has thus been conventionally difficult to allow the main pole to produce a write magnetic field of sufficient magnitude while reducing the length of the magnetic path that passes through the trailing shield and the main pole.
As described above, JP-A-2006-48921A discloses the technology that the two exciting coils, i.e., the trailing-side exciting coil and the leading-side exciting coil disposed with the main pole therebetween, are provided with different numbers of turns so as to produce different magnetomotive forces. The magnetic head disclosed in JP-A-2006-48921A does not include any component that functions as a shield, however. In the magnetic head disclosed in JP-A-2006-48921A, the auxiliary poles are located farther from the main pole than are the exciting coils. In this magnetic head, the distances from the end face of the main pole to the respective end faces of the auxiliary poles are too large for the auxiliary poles to function as shields.